J. C. Kim

Measurement of Thermal Conductivity of TiO2 Thin Films Using 3ω Method

TiO2 film has been used in many industrial components such as laser filters, protection mirrors, chemical sensors, and optical catalysts. Therefore, the thermal properties of TiO2 thin films are important in, e.g., reducing the thermal conductivity of ceramic coatings in gas turbines and increasing the laser damage threshold of antireflection coatings. The thermal conductivity of four kinds of TiO2 thin films, prepared by dc magnetron sputtering, was measured using the 3ω method in the temperature range from 80 K to room temperature. The results showed that the thermal conductivity of TiO2 thin films strongly depends on the thickness and the microstructure of the films. The films with smaller grain size and thinner thickness have smaller thermal conductivities.

Effect of Heat Treatment on Thermal Conductivity of U-Mo/Al Alloy Dispersion Fuel

The molybdenum content of fuel core whose matrix is aluminium 1060, was varied to be 7, 8, and 10 wt% and the volume fraction of U-Mo fuel powders was varied to be 10, 30, and 40 vol%. In this work, thermal conductivities were calculated from measured thermal diffusivities, specific heat capacities, and densities, which were determined using the laser flash, DSC, and Archimedes methods, respectively. The thermophysical properties were measured over a temperature range from room temperature to 500°C. The U-Mo alloy was annealed at between 525 and 550°C for 1 to 36 hours. At high temperature, the U-Mo particles were reacted with aluminium matrix as forming layers of (U-Mo)Alx. These reaction layers have been affected adversely by the thermal conductivity of fuel core. The thermal conductivities of annealed samples appeared to decrease with increasing volume fraction of the reaction layers.

Accurate dew-point measurement over a wide temperature range using a quartz crystal microbalance dew-point sensor

Quartz crystal microbalance (QCM) dew-point sensors are based on frequency measurement, and so have fast response time, high sensitivity and high accuracy. Recently, we have reported that they have the very convenient attribute of being able to distinguish between supercooled dew and frost from a single scan through the resonant frequency of the quartz resonator as a function of the temperature. In addition to these advantages, by using three different types of heat sinks, we have developed a QCM dew/frost-point sensor with a very wide working temperature range (−90 °C to 15 °C). The temperature of the quartz surface can be obtained effectively by measuring the temperature of the quartz crystal holder and using temperature compensation curves (which showed a high level of repeatability and reproducibility). The measured dew/frost points showed very good agreement with reference values and were within ±0.1 °C over the whole temperature range.

Thermal analysis of Tris (8-hydroxyquinoline) aluminum

Abstract In this report, the thermal analysis of Tris (8-hydroxyquinoline) aluminum (Alq 3 ) is presented. The thermal conductivity of Alq 3 , in a temperature range between 300 and 523 K, was determined by measuring its thermal diffusivity and specific heat. The thermal diffusivity measured by the laser flash method is found to decrease with temperature. The specific heat increases with temperature without any trend of saturation until the highest temperature (573 K) was investigated. The room temperature specific heat of Alq 3 is about 1.03 J/g per K and the value at 523 K is about 1.67 J/g per K. A very low thermal conductivity (room temperature) of Alq 3 , 0.107 W/m per K, was determined. The thermal conductivity is found to increase with temperature within the investigated temperature range. The measured thermal conductivity was applied to the modeling of a heat spreading during a device operation.

Ferromagnetic nanospheres of perovskite manganite La0.7Ca0.3MnO3 prepared by template replication in porous carbon framework

Nanospheres of perovskite manganite La0.7Ca0.3MnO3 (LCMO) were prepared using porous carbon replica as a template. Close-packed arrays of silica spheres were infiltrated with a sucrose solution, which was then carbonized. After removal of the silica template, pores in the replica were filled with metal acetate precursors. The filled replica was sintered at 800u200a°C. The resulting hollow LCMO nanospheres were characterized by magnetization, electrical transport, scanning electron microscope, and transmission electron microscope measurements. The magnetization data of LCMO show a ferromagnetic transition near 250 K.

One-level two points method for estimation of thermal diffusivity by the converging thermal wave method

The thermal diffusivity of several kinds of metal sheets was measured by the converging thermal-wave technique. This is a typical technique which can obtain the in-plane thermal diffusivity by measurement of the temperature evolution at the center of the pulsed annular laser beam when the laser beam irradiates the surface of the samples. However, the rapid temperature increase and nonlinearity of the infrared detector in the earlier part, and convection heat loss from the sample surface in the later part, of the temperature evolution can be sources of errors. In this study, when the temperature of the center reached half of the maximum, the timest1andt2, in the ascending and descending parts of the temperature evolution curve, respectively, were determined and other points,t′1andt′2, were determined by increasing the temperature to 90% of the maximum in successive increments of 10% of the maximum. By using these determined times, the variation of thermal diffusivity was investigated and compared with results from existing methods and with reference values.

Recognition of supercooled dew in a quartz crystal microbalance dew-point sensor by slip phenomena

Distinguishing between a supercooled dew and frost below 0 °C in dew/frost-point measurements is an important and challenging problem that has not yet been completely solved. This study presents a new method for the recognition of a supercooled dew in a dew/frost-point sensor. A quartz crystal microbalance (QCM) sensor was used as a dew/frost-point sensor to detect a dew and a supercooled dew as well as frost. The slip phenomenon occurring at an interface between the water droplet and the surface of the quartz crystal resonator of the QCM sensor gives a simple and accurate way of distinguishing between a supercooled dew and frost below 0 °C. This method can give a highly accurate measurement of the dew or the frost point without misreading in the dew-point sensor at temperatures below 0 °C.

Thermal conductivity of CVD diamond films

Diamond films 60 and 170 µm in thickness were grown by PACVD (plasma-assisted chemical vapor deposition) under similar conditions. The thermal diffusivity of these freestanding films was measured between 100 and 300 K using AC calorimetry. Radiation heat loss from the surface was estimated by analyzing both the amplitude and the phase shift of a lock-in amplifier signal. Thermal conductivity was calculated using the specific heat data of natural diamond. At room temperature, the thermal conductivity of the 60 and 170 υm films is 9 and 16 W-cm−1. K−1 respectively, which is 40–70% that of natural diamond, The temperature dependence of thermal conductivity of the CVD diamond films is similar to that of natural diamond, Phonon scattering processes are considered using the Debye model, The microsize of the grain boundary has a significant effect on the mean free path of phonons at low temperatures. The grain in CVD diamond film is grown as a columnar structure, Thus, the thicker film has the larger mean grain size and the higher thermal conductivity. Scanning electron microscopy (SEM) and Raman spectroscopy were used to study the microstructure of the CVD diamond films. In this experiment, we evaluated the quality of CVD diamond film of the whole sample by measuring the thermal conductivity.

Thermal Diffusivity Measurement of Two-Layer Optical Thin-Film Systems Using Photoacoustic Effect1

In this study, we designed and developed two-layer antireflection (AR) optical coating samples on glass substrates, using different evaporation conditions of coating rates and substrate temperatures for two dielectric materials, MgF2 and ZnS, with different refractive indices. The through-plane thermal diffusivity of these systems was measured using the photoacoustic effect. The optical thicknesses of MgF2 and ZnS layers were fixed at 5λ/4 (λ=514.5xa0nm) and λ, respectively, and the thermal diffusivities of the samples were obtained from the measured amplitude of the photoacoustic signals by changing the chopping frequency of the Ar+ laser beam. The results demonstrated that the thermal diffusivity of the sample fabricated under the conditions of 10μÅ·s−1 and 150°C had the maximum value and that the results were directly related to the microstructure of the film system.

Thermal diffusivity measurements of foil-shaped materials by vectorial analysis using an AC calorimeter

Measurements of thermal diffusivity of foil-shaped materials have been carried out using a photoirradiation-type AC calorimeter at room temperature. In this method the frequency effect, which is caused by heat loss from the sample to the environment, is readily detected in measurements of both amplitude and phase components of the AC temperature signal, Even though the chopping frequency is appropriate, the two diffusivities calculated from these two components differ from each other, Moreover, the difference between the two values increases when the chopping frequency increases. Simple vectorial calculation with the two components one from the amplitude and the other from the phase- permits the frequency ellect to be determined. The calculated result is the geometric average of the two diffusivities. This analytic method was tested with diamond film and SUS-304 foil. From these we confirmed that the vectorial analytic method gives similar diffusivity values for different frequencies indicating its reliability.